We have in the prior application, now U.S. Pat. No. 4,058,484 and in application Ser. No. 718,166 cited above disclosed that hydrothermally stable ammonium Y zeolites may be formed by exchange at superatmospheric pressures and suitable reactant ratios. Such zeolites form hydrothermally stable cracking catalysts of high activity.
We have also found that by controlling the pH of the admixture of rare earth and NaX, and NaY, and control of exchange process under such superatmospheric pressure, we obtain rare earth exchanged X faujasite zeolites which may be formulated into hydrothermally stable cracking catalysts of high cracking activity. Reference is made to application Ser. No. 808,268 and copending application Ser. No. 869,856 filed Jan. 16, 1978. The process results in an exchange of sodium to reduce the sodium content to a weight percentage based on the volatile free exchanged zeolite which may be 0.5% or larger without any substantial change in the crystal structure as evidenced by its a.sub.o.
The disclosures in aforesaid patent and applications are hereby incorporated into this application by this reference.
The techniques for carrying out exchanges in the prior art have been described in the prior art (see Rabo "Zeolite Chemistry and Catalysis", page 309 and 310 published by the American Chemical Society in 1976 and see also U.S. Pat. Nos. 3,293,194, 3,402,996, 3,867,277, 3,281,199, 3,169,692 and 2,463,608). Such procedure has also been reported when using an X type zeolite (see U.S. Pat. No. 3,966,882). The literature in this art is extremely voluminous and this statement of the art is not intended to be exhaustive but for the purpose of placing the present invention in the historical perspective of this art.